In recent years, a light emitting diode (LED) using a light guide panel and an organic light emitting diode (OLED, hereafter, it is also called as an organic electroluminescent element) have been attracted attentions as a flat panel light source. An LED with a light guide panel has been used not only for a general illumination, but for various situations and purposes such as a backlight for a liquid crystal display (LCD) (for example, refer to Patent Document 1).
In particular, the production volume of smart devices (smart phones and tablets) has been increased since around the year of 2008. An LED with a light guide panel is used for them. A main use thereof is for a backlight. As other use, an LED with a light guide panel has been incorporated in many cases as a backlight for common function key buttons located in the lower portion of a device.
In many cases, three kinds of marks: home (indicated by a square mark); return (indicated by an arrow mark); and search (indicated by a magnifier mark), are mainly used for common function key buttons.
These common function key buttons have a composition as follows. Generally, a pattern of a required mark is printed on a cover glass. Then, the above-described LED with a light guide panel is placed inside of the cover glass. An LED emits light according to the required situation and the emitted light is guided through the light guide panel (film). The light is taken out to the display side through the light diffusing member having a dot shape and printed on a patterned portion.
However, there are several problems to realize emission of light of the above-described common function key buttons by using an LED light guide panel system.
One of the problems is as follows. The light guide panel (film) is required to be thin since the location space of an LED is limited. When the light guide panel becomes thin, the efficiency of the device with respect to the emission efficiency of the LED light source becomes low.
Another one of the problems is as follows. Since the light is guided from the side of key display, it may produce unevenness of luminance depending on a design or a shape of a key button. When it is intended to solve this unevenness of luminance, it is required to increase the number of the LED sources. This will lead to an increase of cost and an increase of electric power consumption.
Another one of the problems is as follows. It cannot achieve the change of key display corresponding to the situations. When it is intended to realize this, it will result in the composition of laminating a plurality of LED light guide units. This will lead to an increase of thickness and an increase of cost.
Therefore, at present situation, the display of common function key buttons is limited to one kind regardless of the situations. Moreover, it is limited to the key units having pronounced emission unevenness and easily observed the dot shape for guiding light.
There are user's needs of a new common function key unit which enables to solve the above-described three problems. For example, it can suitably change the direction of an arrow mark, it can obtain a uniform light emission without emission unevenness, and it cannot observe the shape of the arrow mark when unlighted. At the present time, these cannot be achieved with an LED having a light guide panel system.
It is possible to form a shape corresponding to the key display by making pattering with a mask during the film forming process of an organic electroluminescent element (organic EL element). However, it was not possible to produce a light-emitting pattern which enables to change an arbitral mark shape at the identical place according to the situation display.
Further, there was a problem that the resolution was insufficient only by making pattering with a mask during the film forming process.